how to create a CityGML format in LOD2?

Hello! I would like to create LOD2 buildings, but somehow, my files don't show their own citygml relations between parent_id and gml_id. Could you find me some errors in my workflow? I created gml_parent_id as a field already.

eg.)

<?xml version="1.0" encoding="UTF-8"?>

<core:CityModel xmlns:brid="http://www.opengis.net/citygml/bridge/2.0" xmlns:tran="http://www.opengis.net/citygml/transportation/2.0" xmlns:frn="http://www.opengis.net/citygml/cityfurniture/2.0" xmlns:wtr="http://www.opengis.net/citygml/waterbody/2.0" xmlns:sch="http://www.ascc.net/xml/schematron" xmlns:veg="http://www.opengis.net/citygml/vegetation/2.0" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:tun="http://www.opengis.net/citygml/tunnel/2.0" xmlns:tex="http://www.opengis.net/citygml/texturedsurface/2.0" xmlns:gml="http://www.opengis.net/gml" xmlns:gen="http://www.opengis.net/citygml/generics/2.0" xmlns:dem="http://www.opengis.net/citygml/relief/2.0" xmlns:app="http://www.opengis.net/citygml/appearance/2.0" xmlns:luse="http://www.opengis.net/citygml/landuse/2.0" xmlns:xAL="urn:oasis:names:tc:ciq:xsdschema:xAL:2.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:smil20lang="http://www.w3.org/2001/SMIL20/Language" xmlns:pbase="http://www.opengis.net/citygml/profiles/base/2.0" xmlns:smil20="http://www.w3.org/2001/SMIL20/" xmlns:bldg="http://www.opengis.net/citygml/building/2.0" xmlns:core="http://www.opengis.net/citygml/2.0" xmlns:grp="http://www.opengis.net/citygml/cityobjectgroup/2.0">

<gml:boundedBy>

<gml:Envelope srsDimension="3">

<gml:lowerCorner>204274.66719240707 554884.0793000031 20.877199999999995</gml:lowerCorner>

<gml:upperCorner>204976.80260000098 555502.5452038753 128.8453</gml:upperCorner>

</gml:Envelope>

</gml:boundedBy>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F063DTEB97RFZJ3NFYM7">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F0637JNZPMTZC8HYSC78">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F064PH5NM9BD0NG5Q2SD">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F065Z619MC6DN9F1T3KY">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F0652WDWV9ER6SSDSDZP">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F066ER6NAP11QN7X3KP8">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F04BHDM8YEMWYTPDNGB6">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F04CVGX5GM33VHN7BHWD">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>

<brid:WallSurface gml:id="GML_01HMZ1F04DQKP18YY3W7SW91A2">

</brid:WallSurface>

</core:cityObjectMember>

<core:cityObjectMember>